1. Technical Field
The present disclosure relates to a high-frequency device. More particularly, the present disclosure relates to a high electron mobility transistor with a superlattice structure.
2. Description of Related Art
For a high electron mobility transistor (HEMT) as a high-frequency device, when a channel layer therein is grown by epitaxy and has a superlattice structure, the composition of the superlattice structure is usually complex and thus difficult to be grown by epitaxy. On the contrary, if purer indium gallium arsenide (InGaAs) is used, for the HEMT having a hetero-structure, the indium (In) content therein may not be high enough so that in the HEMT the electron effective mass is not small enough and the electron mobility is inclined to be low. As a result, the direct-current characteristics and high-frequency characteristics of the HEMT are not better.
On the other hand, the device characteristics mentioned above are closely related to the gate length of the device. However, if the nanometer-scaled gate length is fabricated in order to improve the device characteristics, the electron-beam lithography system has to be used. Thus, the production cannot be raised and the production costs could increase.